Electric linear motors are well known devices, in which one of a coil or magnet element is mounted to a fixed member, and the other element is mounted to a member to be moved. Electric current is applied to the coil, which generates magnetic lines of force to interact with the magnet to produce linear motion of the movable member. Such electric linear motors are generally used in refrigeration compressors in which the movable member is defined by the piston of the compressor and the magnet is mounted to said piston. The coil is fixedly mounted to an external portion of the compressor structure that forms the cylinder, inside which the piston is reciprocated.
FIG. 1 of the appended drawings illustrates a prior art linear compressor of the type disclosed in U.S. Pat. No. 5,945,748. In this known prior art construction, there is provided a hermetic shell 10, within which is mounted a cylindrical inner cup 20 that defines a predetermined inner space. A set of outer laminations 30 for a linear motor is affixed to the inner face of the inner cup 20. A disk shaped cover plate 40 has a hole in a center portion thereof and is connected to a flange 61 that is incorporated to the upper end of a cylinder 60 and to upper end portions of both the inner cup 20 and outer laminations 30. A lower cover 50, which is also disk shaped, is connected to the lower end portion of the inner cup 20. An upper portion of the cylinder 60 extends through the open center portion of the cover plate 40, and a valve system 70 is mounted to the center of the upper portion of the cylinder 60 to tightly cover the hole through which the upper portion of the cylinder 60 extends. A conventional valve plate having suction and discharge valves can also be used. Inside the cylinder 60 is mounted a piston 80 which, upon being reciprocated by the linear motor, compresses a refrigerant gas in a known manner. A set of inner laminations 90 of the linear motor is mounted around a portion of an outer circumferential surface of the cylinder 60, said internal laminations 90 maintaining a predetermined spacing from the set of outer laminations 30.
A coil 95, of toroidal shape, is located in a cut-out portion of an outer circumferential surface of the inner laminations 90, and the ends of the coil 95 are connected to lead wires (not shown) that supply electric current to the coil 95. If desired, the coil 95 can also be located on the set of outer laminations 30. A connecting member in the form of a disk connects the lower end of the piston 80 to a cylindrical actuator 85, to the upper end of which is attached a magnet member 86 usually formed by a plurality of permanent magnets (not shown). The magnet member 86 moves in the space between the sets of outer laminations 30 and inner laminations 90.
As seen from FIG. 1, the linear motor includes the set of outer laminations 30, the set of inner laminations 90 carrying the coil 95, and also the actuator 85, to which the magnet member 86 is attached.
Inner helical springs 66 are provided between the connecting member 65 and a support 68 that is affixed to the bottom of the set of inner laminations 90 to elastically support the reciprocation of the piston 80. Outer helical springs 67 are disposed between the connecting member 65 and the lower cover 50 to support the compressor as the piston 80 reciprocates. At least one refrigerant gas path 80a is provided along an upper portion of the cylinder 60 for admitting refrigerant gas into the latter at a determined position of the piston 80.
In the operation of the compressor illustrated in FIG. 1, when electric current is supplied to the coil 95, the magnet member 86, mounted to the actuator 85, reacts with the magnetic lines of force and reciprocates the actuator 85 in a straight line between the inner laminations 90 and the outer laminations 30, whereby the piston 80 is reciprocated in the cylinder 60 as a function of the corresponding displacement of the actuator 85. The refrigerant gas flows into the cylinder 60 through the refrigerant gas paths 80a provided in the cylinder 60. The refrigerant gas compressed in the cylinder 60 is discharged through the valve system 70, and the above described operation is repeatedly performed.
The inner laminations 90 may be mounted to the cylinder by using any one of the constructions presently known, such as the one illustrated in FIG. 1. For example, there can be provided a molded bracket member mounted to the cylinder and carrying the inner laminations 90, these laminations having a cut-out in the outer surfaces thereof for lodging the coil 95.
FIG. 1A illustrates a type of mounting that can be used for mounting the outer laminations 30. This figure illustrates a modification of an arrangement shown in said US patent. The outer laminations 30, made of a magnetic metal, such as iron or steel, are radially disposed relative to the center of the compressor. A tubular frame 25 is mounted internal of the wall of the inner cup 20 and carries a shelf 26 onto which is mounted the lower end of each outer lamination 30, and the tubular frame 25 is further provided with an upper bracket 27 to connect the upper end of the outer laminations 30. Nevertheless, it should be understood that any suitable mounting arrangement might be used for adequately securing the outer laminations 30 to the wall of the inner cup 20.
As seen in the compressor of FIG. 1, the cylinder 60 is formed with a flange 61 extending radially outwardly from the top of the cylinder 60, and the cover plate 40 provides a connection between the flange 61 of the cylinder 60 and the outer laminations 30. As described below, this known construction gives rise to various problems.
FIG. 2 shows a part of another type of prior art compressor formed by a cylinder 60, to whose outer face is affixed, by glue or any other fixing means, a linear motor, whose stator comprises inner laminations 90 having an external cut-out for housing a toroidal coil 95, as already described in relation to FIG. 1. The upper ends of a set of outer laminations 30 are directly affixed, by glue, welding or any other fixing means, to the inner surface of an external portion of a flange 61 incorporated to the cylinder 60 and extending radially outwardly therefrom, in order to provide a suspension mounting to the outer laminations 30. The lower surface of the flanges 61 also contacts the tops of the inner laminations 90. Thus, there is provided a direct connection between the flange 61 of the cylinder 60 and the outer laminations 30 and the inner laminations 90.
Heretofore the linear motor has been described as used in a linear compressor. However, such linear motors also find use in other devices. For example, a stationary bushing can replace the cylinder 60 of the compressor and the piston of the latter can be replaced by a shaft that can be reciprocated to perform a determined work as the linear motor operates. Such other devices may require arrangements for mounting the inner and outer laminations, and may present variations in the structural configurations thereof in relation to those illustrated in FIGS. 1, 1A and 2. However, all these known variations use a direct connection between the three components that are, (or correspond to, in other devices) the cylinder 60 with its flange 61, the inner laminations 90, and the outer laminations 30 of the linear motor.
Such constructions, which are described particularly for the linear compressor, but have equivalent components in other useful devices, have the following disadvantages:                a large amount of material is required for constructing the cylinder, since the cylinder must incorporate its radially outwardly projecting flange 61. Moreover, in the embodiment illustrated in FIG. 1, it is further required the provision of the cover plate 40.        the cylinder must be made of a non-magnetic material, in order to avoid the flow of magnetic lines of force through the structure. This would generate Foucault currents producing heat and energy loss.        the non-magnetic materials for producing the cylinder are usually of the austenitic type, or of various types of stainless steel or aluminum, among others, and all such materials being relatively expensive.        the construction of the cover plate 40 and the flange 61 of the cylinder 60 present a large surface, causing undesired irradiation of noise.        a large number of machining operations is needed to form the cylinders illustrated in FIGS. 1 and 2, as well as a large amount of investment in equipment to produce the cylinders.        some non-magnetic materials used to produce the cylinder are inadequate for the components to be subjected to friction, as it occurs, for example, between the reciprocating piston and the cylinder, or between the reciprocating shaft and the stationary bushing, making necessary, in certain cases, to use a sleeve of a harder material for the cylinder or bushing. This makes the mounting operation more difficult, increasing the cost of the final product.        